Ionic channels in the cell membranes of neurons play a crucial role in cell function, but channels in central neurons are still poorly understood. Besides mediating the electrical behavior of neurons, ionic channels in neurons play a critical role in regulating the intracellular concentration of calcium, increasingly recognized as an important second messenger. The long-term goal of the proposed research is to use patch clamp techniques to characterize the types and functional properties of ionic channels in neurons of the mammalian central nervous system, especially those channels that are important for regulating calcium entry. The work will focus on neurons in the rat hippocampus. The specific aim of this project is to use a pharmacological approach to characterize two types of channels that are known to be important for calcium influx: voltage-dependent calcium channels and NMDA receptor channels. The pharmacology of calcium channels will be studied using a variety of organic compounds, including toxins from spider venom, with a two-fold goal: to use pharmacological agents to help distinguish the different kinds of voltage-dependent calcium channels present in hippocampal neurons and to determine which channel types play a role in specific cellular functions, such as synaptic transmission. The block of NMDA receptor channels by organic compounds will also be studied, with the focus on drugs like the anti-convulsant MK-801 that may block by interacting with the ion permeation pathway of the channel. The goal will be to characterize the drug:channel interaction by determining the potency, kinetics, sidedness, pH-dependence, and voltage-dependence of drug block. The development of specific pharmacological probes for individual channel types that mediate calcium entry will make it possible to explore which channels mediate calcium entry in cultures of interacting neurons under both physiological and pathological conditions; this work will be undertaken in collaboration with the Furshpan laboratory. Excessive calcium entry has been implicated in cell death resulting from stroke or cardiac arrest. Existing calcium channel blocking drugs have shown clinical promise as neuroprotective agents and also in treatment of epilepsy and alcohol withdrawal syndrome. Better understanding of calcium entry pathways and their block by drug molecules should help lead to better pharmacological agents for the treatment of these clinical states.